Insertable stator vane assembly

ABSTRACT

A turbofan engine fan stator assembly includes stator vanes readily insertable through the outer shroud into the stator assembly hub. Elastomeric grommets seal between the vanes, shroud and hub, and an outer band radially inwardly compresses the assembly. The vanes are radially secured to the hub only through frictional engagement with the hub grommet.

TECHNICAL FIELD

This invention relates to gas turbine engines, and relates moreparticularly to a stator vane apparatus and assembly method for use insuch a gas turbine engine.

BACKGROUND OF THE INVENTION

Turbofan gas turbine engines include a forwardly located, high speedrotary fan which receives, compresses, and discharges the primary airflow of the gas turbine engine to produce power, either in the form ofthrust for an aircraft or to produce rotary mechanical power. Disposedimmediately downstream of the fan is a fan stator assembly comprising aplurality of stator vanes spanning the duct carrying the compressed airflow from the fan. The stator vanes operate to redirect the directionand amount of swirl imparted to the compressed air such that if is inproper swirl orientation for the next stage of engine operation and/orto straighten bypass airflow. Normally the following stage is the firststage of a high pressure compressor. It is important that the mass ofsuch a stator vane assembly be minimized to minimize overall weight ofthe engine, yet be tolerant of foreign object damage which may occurwhen foreign objects are carried through the fan in the inlet air flow.

Typically, the complexity of such a fan stator assembly requires verylengthy assembly time due to the number of components. For example,sixty to eighty stator vanes are not uncommon for such a fan statorassembly. Complexity and the length of time for assembly directlycontributes to the overall cost of the engine. Repair and overhaul oftypical stator assemblies cannot be accomplished except at the site oforiginal manufacture.

SUMMARY OF THE INVENTION

It is an important object of the present invention to provide animproved stator vane assembly structure, and method of assembling, whichdramatically reduces overall assembly time by utilizing stator vanesthat are readily insertable radially through the outer shroud and intothe inner hub.

Another important object of the present invention is to provide animproved stator vane assembly of the type described which, by virtue ofits assembly techniques, does not rigidly intersecure the inner radialtip end of the stator vanes to the hub, to provide a controlled,predictable vane failure in the event of foreign object damage toprevent further damage to the engine and to allow continued operationthereof.

Another important object of the present invention is to provide animproved stator vane assembly of the type referred to wherein the statorvane is of a light weight, composite, nonmetallic material resistant toerosion, and subject to a controlled, predictable failure in the eventof foreign object damage.

These and other objects and advantages of the present invention arespecifically set forth in, or will become apparent from the followingdetailed description of a preferred embodiment of the invention, whenread in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial side elevational, cross sectional view of a portionof a gas turbine engine incorporating the present invention;

FIG. 2 is an exploded perspective view of partially assembled elementsof the fan stator assembly of the present invention, with portionsbroken away to reveal internal details of construction;

FIG. 3 is a partial plan cross sectional view of a typical stator vane,as viewed along lines 3--3 of FIG. 1;

FIG. 4 is an enlarged partial elevational cross sectional view of thearea denoted by lines 4--4 of FIG. 1;

FIG. 5 is a view similar to FIG. 4 but showing the area denoted by lines5--5 of FIG. 1;

FIG. 6 is a top plan view of the foot portion of a stator vane as viewedalong lines 6--6 of FIG. 1;

FIG. 7 is a top plan view of the hub grommet;

FIG. 8 is an elevational cross sectional view taken along lines 8--8 ofFIG. 7;

FIG. 9 is a top plan view of the outer grommet seal;

FIG. 10 is an elevational cross sectional view taken along lines 10--10of FIG. 9; and

FIG. 11 is a partial front elevational view of a portion of the statorvane assembly, with a failed vane illustrated in dotted lines.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to the drawings, a turbofan gas turbineengine generally referred to by the reference numeral 20 includes anouter casing 22, a rotary front fan 24, and a stator vane assembly 26disposed immediately downstream of the blades 25 of the fan 24. Thestator vane assembly is secured to the outer casing 22 in stationaryrelationship, and is also affixed to internal stationary supportstructure 28 of the engine. Downstream of the stator vane assembly 26,the compressed air flow may be split by a divider 30 into a core airflow passage 32 leading to the compressor stages of the gas turbineengine, and a bypass duct 34 wherein air flow may be exhausted out therear of the engine.

As best depicted in FIGS. 1, 2, 6 and 11, the stator vane assembly 26includes an annular or circular outer shroud 36 having opposed axialends secured by conventional structure to casing 22. Additionally, thestator vane assembly 26 has an annular, metallic inner hub 38 secured tosupport structure 28. Spanning the radial space between shroud 36 andhub 38 are a plurality of stator vanes 40 having a radially inner tipend 42 extending through openings 44 in hub 38, and an opposite outerend of each of the vanes 40 is formed with an integral foot 46 locatedoutwardly of the outer surface of shroud 36. Shroud 36 has similaropenings 37 therein through which the aerodynamically contoured portionof the vanes 40 may be inserted, as described in greater detail below.

As illustrated in FIG. 3, the stator vane 40 is preferably comprised ofa nonmetallic, composite material consisting of a plurality ofcompression molded, heat cured plies. The plies include up to sevencentrally located plies of reinforcement material such as aunidirectional yarn of para-aramid fiber, such as Kevlar (a trademark ofE. I. DuPont Demours & Company). The plies of para-aramid fibers 48 arenonwoven with the orientation of the inner directional yarns thereofsubstantially in alignment with the longitudinal, longest, axis of thevane 40. On each side of the centrally located plies of para-aramidfibers are a plurality of plies of resin impregnated graphite fibermaterial 50 and 52. These plies 50 are also nonwoven, unidirectional anddivided in to two sets of plies. The first set of plies 50 of thegraphite fibers are oriented at an acute angle of approximately 22degrees to the orientation of the centrally located fibers 48. The outerset of plies 52 have an orientation of approximately 55 degrees relativeto the orientation of the centrally located fibers 48. The set 50comprises at least two plies of such graphite fibers, and the set 52 oneach side of the centrally located fibers 48 also comprises at least twoplies of the graphite fiber material. Acceptable graphite material isavailable from Hexcel Corp., Dublin, Calif. A ply of woven steel wiremesh material 54 is placed on the external surface of the vane 40 incovering relationship to the leading edge thereof. All of the plies 48,50, 52 and 54 are compression molded and heat cured in the sameoperation. The result is a strong, light weight composite material forvane 40.

The stator vane assembly 26 further includes an inner seal in the formof a hub grommet 56 illustrated in detail in FIGS. 5, 7 and 8. Grommetseal 56 is comprised of a flexible thermoelastic ether-ester elastomer,(such as "HYTREL" available from DuPont referenced above) material andhas radially inner and outer lips 58, 60 overlying the inner and outersurfaces of hub 38 and extending through each of the openings 44.Grommet 56 has a central opening 62 closely configured to the inner tip42 of the vane 40 for snugly, sealingly and receiving the same. It isimportant to note that vane 40 is radially restrained to hub 38 solelyby frictional engagement with, and compression of grommet 56.

Disposed between the foot 46 of vane 40 and the outer surface of outershroud 36 is a shroud grommet 64, also of flexible thermoelasticether-ester elastomer material, disposed on the exterior surface ofshroud 36 between it and the foot 46 of vane 40. Grommet 64 overlies aportion of the outer surface of shroud 36 to sealingly engage thelatter, and also includes a radially inwardly extending lip 66 whichclosely surrounds and sealingly contacts the radially outermost portionof the air foil section of the vane 40. Grommet 64 also has an opening68 therein through which the aerodynamic portion of the vane extends.

Foot 46 of each vane 40 extends radially and circumferentiallytherefrom, and includes a circumferentially extending central groove 70therein. Disposed within groove 70 is a layer of protective tape 72 suchas 3M type 25 tape, and a circular, annular band of metallic material 74that extends around the entire circumference of the stator vane assembly26. As described in greater detail below, the band 74 includes a strap76 configured into a circular arrangement with opposing ends 80 thereofin approximately abutting engagement, and an overlying strip of metallicmaterial 82 which is blind riveted at 84 and 86 to the opposed ends 80of the strap 76 to hold the same in circular configuration, for purposesas described in greater below.

The fan stator assembly 26 may be conveniently and rapidly assembled inthe following manner. First, the inner and outer shrouds 36, 38 aredisposed in an assembly fixture (not shown) in the appropriate relativeaxial, concentric arrangement to one another, and circumferentiallyclocked with the associated openings 37, 44 thereof aligned radially. Astator vane 40 is assembled in the following manner. First, hub grommet56 is mounted onto the hub 36 with the inner and outer lips thereof insurrounding, overlying relationship to the opening 44 therein. Also, theshroud grommet 64 is slipped loosely onto the stator vane 40 and pushedto a location somewhat adjacent the outer foot 46 thereof. The inner end42 of the vane 40 is then inserted radially inwardly through opening 37in outer shroud 36. FIG. 2 illustrates this partially assembled state.Then end 42 is pushed further radially inwardly through the opening 62in the hub grommet 58 such that the inner tip end 42 of the vane extendsslightly radially inwardly of the grommet 56. In this position of vane40 the major radially and circumferentially extending sealing surface ofgrommet 64 is in abutting engagement with the radial inner surface offoot 46.

Each stator vane is sequentially inserted through the associatedopenings 37, 44 in the manner described above, until all stator vanes,grommets 56, and grommets 64 are in position. An assembly clamping tool(not shown) is then brought into engagement with the radial outersurfaces of the foot 70 of all the stator vanes 40. In this dispositionthe adjacent foot of each stator vane has the grooves 70 thereof alignedwith one another to present a full circular, circumferential grooveextending around the outer circumference of the assembly. Preferably,the clamping mechanisms may be disposed on opposite sides of the grooves70 and extend circumferentially around the entire assembly. The clampingmechanism is then actuated to exert a uniform, radially inwardlydirected, clamping force on the entire assembly. A clamping force ofapproximately 200 psi has been found adequate. Various types of assemblyclamping mechanisms could be utilized. For example adjustable diametercircular bands could be placed around the assembly, then reduced indiameter to create the radial inward clamping force on the assembly.

Protective tape 72 is then positioned in the bottom of the alignedgrooves 70, and band 74 is then placed upon the tape 72, positionedwithin the aligned grooves 70. Band 74 extends around the entirecircumference of the assembly. The opposed ends of the strap 76 arebrought adjacent one another, snugly lying within the aligned grooves70. Strip 82 now overlies the opposed ends 80 of the strap 76, and blindrivets 84, 86 are installed from the radial outer direction to firmlyintersecure the opposed ends of the strap 76. If desired, one end of thestrip 82 may be pre-secured to one end of the strap 76 through blindrivets 84, requiring only the installation of the other set of blindrivets 86 to complete the securement of band 74 in to the alignedgrooves 70.

Once the opposed ends 80 of strap 76 are so intersecured by installationof strip 82, band 74 is now holding the assembly with the radial inwardclamping force still applied. The temporary assembly clamping mechanismmay then be removed, and the radial inward clamping force on theassembly is still retained by virtue of band 74. In such position, outergrommet 64 is in adequate sealing interengagement with foot 70 andshroud 36 to preclude air leakage through the openings 37 in shroud 36.Similarly, vane 40 is in frictional, sealing interengagement with thewalls of opening 62 in hub grommet 56, also pressing grommet 56 intosealing interengagement with hub 38. As a result, hub grommet 56effectively precludes air leakage through the openings 44 in hub 38.

It is important to note that the inner tip end 42 of the vane 40 is notrigidly intersecured upon hub 38. Rather, each of the vanes 40 isradially held in place in the hub 38 solely by the frictionalinterengagement of the vane 40 with the grommet 56. It will now be clearthat this radial nonsecurement of the vanes 40 to the hub 38 allows andfacilitates the simplified, convenient, and rapid assembly of the entirestator vane assembly 26.

During operation of the gas turbine engine, foreign objects may beingested through the inlet of the engine, passing by the primary fanblades 25 and impacting upon one or more of the vanes 40 of stator vaneassembly 26. In aerospace applications, such gas turbine engines must beable to withstand foreign object damage up to a certain size, and theengine must continue to operate, perhaps on a reduced efficiency basis,for a predetermined period of time for safety of the aircraft.

The stator vane assembly 26 of the present invention facilitates safetyand operation of the engine in the event of ingestion of foreignobjects, by virtue of the structure and configuration of the stator vaneassembly 26 as set forth previously. More particularly, a typicalfailure as may be expected to occur due to foreign object damage impactis illustrated in dashed lines in FIG. 11. Here, a stator vane 40a hasbeen impacted by an injected object and broken by the impact of theobject. By virtue of inclusion of the reinforcement plies 48 centrallydisposed within the stator vane 40a, this stator vane, though crackedand broken, remains in a single piece. A portion of the stator vane isnot completely broken off to be carried inwardly through the engine tocreate yet further damage.

Importantly, because the inner end of the stator vane is only radiallyretained by the frictional contact with the associated grommet 56, thisinner end is pulled out of and released from hub 38 as a sequence offailure occurrences caused by impact from the foreign object. Becausethe inner end of the blade 48 is rather readily released from the hub 38in this failure sequence, the failed blade 40a rotates and twists in adown stream direction to relatively minimize air flow blockage throughthe stator vane assembly, yet the broken stator vane 40a is retained inthe stator vane assembly 46 by virtue of the intersecurement of the footthereof to the outer surface of shroud 36 as created by the radialinward compression force being exerted thereon through band 74.

For field repair and overhaul purposes, the present invention offersfurther advantage. The stator vane assembly 26 may be readilydisassembled in the field by reversing the assembly steps noted above.That is, a clamping fool is inserted about the circumference to allowrivets 86 to be removed from one end of strip 82 and thus release strap76 and permit removal of band 74. One or more damages vanes 40 may thenbe replaced. In comparison, prior art stator, vane assemblies, withtheir weldments, potting, etc., normally require the entire stator vaneassembly to be returned to the manufacturer, and a plurality of assemblycomponents are required to be replaced even if only one vane requiresreplacement.

Various alterations and modifications to the preferred arrangement ofthe invention will be apparent to those skilled in the art. For example,the assembly method and technique could be utilized with metallic,rather than composite stator vanes. Accordingly, the foregoing detaileddescription should be considered exemplary in nature and not as limitingto the scope and spirit of the invention as set forth in the appendedclaims.

Having described the invention with sufficient clarity that thoseskilled in the art may make and use it, what is claimed is:
 1. In a gasturbine engine having a rotary primary fan and a stationary fan statorvane assembly disposed downstream of said fan, said assemblycomprising:an annular outer shroud having openings therein; an annularinner hub having openings therein and disposed concentrically to andradially inwardly of said shroud to define a radial space therebetween;a plurality of stator vanes having air foil sections extending acrosssaid radial space and through said openings in said shroud and hub, eachof said vanes having a radial inner and extending through the associatedone of said openings in the hub, and an axially and circumferentiallyextending foot on the opposite radial outer end, said foot disposedradially outside said shroud; an inner compressible seal between saidhub and each of said stator vanes for sealing said associated openingsin the hub, said stator vanes being in frictional engagement with theassociated inner seal; an outer compressible seal between said shroudand the foot of each of said stator vanes for sealing said associatedopenings in the shroud; and means encircling said stator vanes andengaging said foot of each for exerting a radial inwardly directedcompression force thereon to intersecure said assembly, said vanes beingcomprised of a nonmetallic composite material comprising a plurality ofcompression molded, heat cured plies, said plies including a pluralityof centrally located internal plies of reinforcement material ofunidirectional yarns of para-aramid fibers, a plurality of plies ofresin impregnated graphite fiber material on each side of said centrallylocated plies of reinforcement material, and an external steel wire meshply on the leading edges of said vanes.
 2. A gas turbine engine as setforth in claim 1, wherein said means for exerting a radial inwardlydirected compression force comprises an annular metallic band extendingcircumferentially around said assembly.
 3. A gas turbine engine as setforth in claim 2, wherein said vanes have a circumferentially extendinggroove on the outer surface of said foot, said grooves being aligned toreceive said band.
 4. A gas turbine engine stator vane assemblycomprising:an annular outer shroud having openings therein; an annularinner hub having openings therein and disposed concentrically to andradially inwardly of said shroud to define a radial space therebetween;a plurality of stator vanes having airfoil sections extending acrosssaid radial space and through said openings in said shroud and hub, eachof said vanes having a radial inner and extending through the associatedone of said openings in the hub, and an axially and circumferentiallyextending foot on the opposite radial outer end, said foot disposedradially outside said shroud; an inner compressible seal between saidhub and each of said stator vanes for sealing said associated openingsin the hub, said stator vanes being in frictional engagement with theassociated inner seal and being otherwise unsecured to said hub; anouter compressible seal between said shroud and the foot of each of saidstator vanes for sealing said associated openings in the shroud; andmeans encircling said stator vanes and encircling said foot of each forexerting a radial inwardly directed compression force thereon tointersecure said assembly, said vane comprised of a nonmetalliccomposite material comprising a plurality of compression molded, heatcured plies, said plies including a plurality of centrally locatedinternal plies of reinforcement material of unidirectional yarns ofpara-aramid fibers, a plurality of plies of resin impregnated graphitefiber material on each side of said centrally located plies ofreinforcement material, and an external steel wire mesh ply on theleading edges of said vanes.